The present invention pertains to the image display art. It finds particular application in conjunction with the display of CT medical diagnostic images on video monitors and will be described with particular reference thereto. However, it is to be appreciated that the invention is also applicable to medical diagnostic images from magnetic resonance, nuclear, and other imaging modalities, to quality assurance and other three-dimensional, non-medical images, and the like. The invention is also applicable to hard copy displays, film image displays, and other display formats.
Heretofore, CT scanners have irradiated a planar region of a subject from various angles and detected the intensity of radiation passing therethrough. From the angle and radiation intensity information, two-dimensional image representations of the plane were reconstructed. A typical image representation included a 512.times.512 pixel array, although coarser and finer arrays are also known.
For three-dimensional imaging, the patient was moved along a longitudinal axis of the CT scanner either continuously for spiral scanning or incrementally, to generate a multiplicity of slices. The image data was reconstructed, extrapolating or interpolating as necessary, to generate CT numbers corresponding to each of a three-dimensional array of voxels. For simplicity of illustration, each of the CT numbers can be conceptualized as being addressable by its coordinate location along three orthogonal axes, e.g. x, y, and z-axes of the examined volume.
Typically, the volume data was displayed on the planar surface of a video monitor. Various planar representations of the volume data are now commonly available. Most commonly, the examined volume was a six sided prism with square or rectangular faces. The operator could select a display depicting any one of the six faces of the prism or any one of the slices through an interior of the prism along one of the (x,y), (x,z) or (y,z) planes. Some display formats also permitted oblique planes to be selected. Display formats were also available which permitted two or three sides of the prism to be displayed concurrently on a two-dimensional (i,j) image plane with appropriate visual cues to give the impression of a perspective view in three dimensions. That is, the visible faces were foreshortened (or extended) and transformed from rectangles to parallelograms by a sine or cosine value of an angle by which the viewing direction was changed. In this manner, each face of the prism was transformed into its projection along the viewing direction onto the viewing plane. This gives the faces the appearance of extending either parallel to the viewing plane or video monitor screen or extending away from the screen at an oblique angle. Some routines added shading to the view to give further visual cues of depth.
More specifically, the operator could typically cause a selected surface, such as a transverse (x,y) plane on the face (z=0) of the examined volume to be displayed. The operator could then cause a selected number of transverse planar slices to be peeled away or deleted by indexing along the z-axis (z=1,2,3, . . . ,n) to view the nth interior transverse planes. The operator could then position the cursor on the (x,y) or transverse plane to select a coronal or (x,z) plane. The selected coronal plane would then be displayed. The operator would then position the cursor on the displayed coronal plane to select a sagittal or (y,z) plane. Prior art medical image workstations commonly permitted the transverse, coronal, or sagittal planes or views to be displayed concurrently on the same screen. Some also permitted the three-dimensional projection image to be displayed concurrently as well.
One of the disadvantages of these prior art systems is that they did not permit simultaneous, interactive adjustment of the selected transverse, coronal, and sagittal planes. These prior art adjustments were commonly based on a two-dimensional reference plane which was always co-planar with the transverse, sagittal, or coronal planes, therefore restricting the sectioning cursor to two-dimensional movements. In the display format in which all three planes were displayed concurrently, the operator moved the cursor to one of the views, which then became the "active" view. By moving the cursor on the active view, the next planar slice could be reselected. By moving the cursor to the readjusted planar slice, the next slice could be readjusted. Thus, readjusting the displayed transverse, coronal, and sagittal views was sequential and, therefore, relatively slow and time consuming.
The present invention contemplates a new and improved method and apparatus for displaying images which permits concurrent, real-time readjustment of the transverse, coronal, and sagittal view displays by using a rotatable 3D object (or volume) and its projection view as a three-dimensional reference surface which allows the sectioning cursor to move in three dimensions.